What does the term "support loop" specifically mean?
Basically, support loops mainly apply when using a Subdivision Surface modifier. Loosely put, the modifier acts to take an &quot;average&quot; of the angle between two faces, and then creates a curve to smoothly transition between the normal vectors of the two faces. See the images below:


By adding loop cuts or &quot;support loops&quot;, you can control the size (area) of the faces that are being averaged (in one direction only if necessary) which in turn affects the degree of the averaging.

By adding more loops, or changing their position, you can change the &quot;roundness&quot; of your object. This is often used as a method to sharpen the corners of objects with a Subdivision Surface modifier applied. If you look at the effect of the two loops near the &quot;corner&quot;, you can see that this is similar to how the Bevel Modifier works (by default) to sharpen edges.